The present disclosure relates generally to an electroplating system and a method for using the electroplating system. More particularly, the present disclosure relates to techniques for controlling the concentration of organic additives in an electroplating solution used in an electroplating system.
Generally, an electroplating system is configured to deposit a layer of a metal as a plating material on top of a workpiece that is a different metal to modify one or more surface properties of the workpiece. The workpiece is placed in an electroplating tank containing an electroplating solution. An electrical circuit is created when a negative terminal of a power supply is connected to the workpiece so as to form a cathode and a positive terminal of the power supply is connected to another metal in the electroplating tank so as to form an anode. Electroplating material, typically a stabilized metal ion, is provided in the electroplating solution. During the electroplating process this metal ion is replenished with a soluble metal that forms the anode and/or can be added, directly to the electroplating solution (e.g., as a metal salt). When an electrical current is passed through the circuit, metal ions in the electroplating solution take-up electrons at the workpiece and a layer of metal is formed on the workpiece.
Electroplating solutions can contain organic additives. Different kinds of organic additives are used in electroplating solutions. A first kind or organic additive is referred to as a “brightener.” A brightener makes a plating film dense and improves its luster. An example of a brightener is mercaptoalylsulfonic acid (HS—CnH2n—SO3). This substance exists as an anion in, for example, a copper sulfate plating solution, and prevents the precipitation of a copper ion and promotes its fine division. A second kind of organic additive is referred to as a “suppressor.” A suppressor is adsorbed to a cathode surface and suppresses the precipitation of a metal ion to enhance activation polarization and raise uniform electrodensity. Examples of a suppressor include polyethylene glycol (PEG) and polypropylene glycol (PPG). A third kind of organic additive is referred to as a “leveler.” A leveler is an organic compound containing nitrogen or oxygen that tends to decrease electroplating rate. An example of a leveler additive is a polyamine.
In electroplating systems, the concentration of organic additives must be closely controlled in the low parts per million range in order to attain desired deposition properties and morphology.